The Impact of Iodine Prophylaxis on Thyroid Volume in Schoolchildren Living in a Previously Mild-to-Moderate Iodine Insufficiency Area

Presentation Number: OR38-6
Date of Presentation: April 3rd, 2017

Malgorzata Trofimiuk-Müldner*1, Zbigniew Szybinski2, Monika Buziak-Bereza1, Grzegorz Sokolowski3, Andrzej Lewinski4, Arkadiusz Zygmunt4, Krzysztof Sworczak5, Marek Ruchala6, Elzbieta Bandurska-Stankiewicz7, Filip Golkowski8 and Alicja Bronislawa Hubalewska-D1
1Jagiellonian University Medical College, Krakow, Poland, 2Polish Council for Control of Iodine Deficiency Disorders, Poland, 3University Hospital in Krakow, Krakow, Poland, 4the Polish Mother’s Memorial Hospital- Research Institute, Lodz, Poland, 5Medical University of Gdansk, Gdansk, Poland, 6Poznan University of Medical Sciences, Poznan, Poland, 7University of Warmia and Mazury, Faculty of Medical Sciences, Olsztyn, Poland, 8Jagiellonian University Medical College, Faculty of Medicine, Krakow, Poland

Abstract

Poland was considered as a mild-to-moderate iodine deficiency area according to results of a nation-wide survey conducted in early 1990-ties. The obligatory iodine prophylaxis program based on iodization of house-hold salt (30 mg of iodide/1 kg of salt) was therefore introduced in 1997. However, according to the current WHO-endorsed ultrasonographic thyroid volume (TV) reference, Polish schoolchildren remain iodine deficient.

The aim of the study was to assess the real impact of the Polish iodine prophylaxis model on thyroid volume in schoolchildren.

Material and methods: The study included 9210 Polish schoolchildren (4731 girls, 4479 boys) aged 6-12 years, examined between 1999 and 2011. The informed written parental consent for participation in the survey was obtained for each child. 3803 of children (1909 girls and 1894 boys) were born at least one year after introduction of the iodine prophylaxis (after 12/31/1997), which meant that their mothers were using iodized salt while being pregnant. In each child TV was assessed by ultrasound (7.5 MHz linear probe) and calculated according to Brunn’s formula. Body surface area (BSA) was calculated according to the following formula: weight (kg)0.425 * height (cm)0.725 * 71.84 * 10-4.  Thyroid volume was then standardized to body surface area (TV in ml divided by BSA in m2) to minimize the influence of child age. Urinary iodine concentration (UCI) in urine casual sample was measured by Sandell-Kolthoff method.

Results: The median standardized thyroid volume (TVs) was 3.96 ml/m2 (LQ – 3.12 ml/m2, UQ – 4.91 ml/m2, respectively). The median UCI was 96.2 mcg/L (LQ – 64.0 mcg/L, UQ – 142.6 mcg/L, respectively). There was statistically significant correlation between UCI and TVs (R square 0.010 for logarithmic correlation, p<0.001). TVs in children born after introduction of iodine prophylaxis was significantly lower (mean 3.9 ± 1.24 ml/m2 vs. 4.29 ± 1.69 ml/m2, p<0.001, Mann-Whitney U test). The statistically significant difference in TVs according to time of birth was seen both in girls (mean 3.97 ± 1.35 ml/m2 vs. 4.47 ± 1.83 ml/m2, p<0.001) and boys (mean 3.83 ± 1.12 ml/m2 vs. 4.10 ± 1.50 ml/m2, p<0.001). UCI was significantly higher in children born after introduction of obligatory iodine prophylaxis (mean 118.23 ± 74.68 mcg/L vs. 104.59 ± 66.80 mcg/L, p<0.001, Mann-Whitney U test; mean 115.69 ± 74.31 mcg/L vs. 102.41 ± 66.09 mcg/L, p<0.001, and mean 120.78 ± 74.99 mcg/L vs. 106.97 ± 65.30 mcg/L, p<0.001, for girls and boys respectively). In spite of thyroid volume standardization, children age may be a confounding factor.

Conclusions: Iodine prophylaxis based on iodization of household salt is effective in reduction of thyroid volume in children living in an area previously considered mildly-to-moderate iodine deficient.

 

Nothing to Disclose: MT, ZS, MB, GS, AL, AZ, KS, MR, EB, FG, ABH